For the purposes of reducing the weight as compared with members using an aluminum alloy plate singly and further imparting damping performance and noise insulation performance and the like, there have hitherto been proposed composite panels which are a lightweight composite formed article in which a resin having foamable property is interposed as a core between two aluminum alloy plates and laminated.
In order to manufacture such a lightweight composite formed panel, first of all, a resin having foamable property (foamable resin) is interposed as a core between two flat aluminum alloy plates via an adhesive resin and laminated, thereby bonding and integrating the laminate as an unfoamed laminated plate. Thereafter, this unfoamed laminated plate is formed into a desired shape by press forming or roll forming. After or before this forming, the resin having foamable property is foamed by heating at a foaming temperature of the resin having foamable property, which is higher than that at the time of bonding. The resin having foamable property as referred to herein means a resin which is foamed by heating or a resin which is foamable by heating.
With respect to this basic structure, for the purpose of enhancing various properties of composite plates, such as appearance, light weight, impact resistance, heat resistance, heat retaining properties, and durability, it is proposed to control the foaming magnification of a foamed resin and to laminate a foamed resin having a different foaming magnification (see Patent Document 1). Also, in order to suppress the separation of a layer of a resin having foamable property from inner surface of aluminum alloy plate after foaming, it is proposed to allow an adhesive layer and a resin having no foamable property layer to intervene between an aluminum alloy plate and a resin having foamable property layer (see Patent Document 2).
Here, as specific applications, if such a lightweight composite plate can also be applied in the field of automobile body panels, it is possible to contrive to reduce the weight of the body and to enhance fuel consumption and drivability. But, as is well known, automobile body panels such as outer panels or inner panels, e.g., hoods, doors, etc., roof panels, undercover panels, deck boards, and bulkheads have a relatively large area of 2 m2 or more and have a complicated shape and a large forming area. For that reason, even in a steel plate which is actually used as such an automobile body panel material, or an aluminum alloy plate which is inferior in formability to the steel plate, there may be the case where press forming such as bulging, and deep drawing is relatively difficult.
In this regard, in the case where the shape is relatively simple as in noise absorbing members or damping members of automobiles or the like, or in the case where the forming area is small, it is possible to form the lightweight composite plate having a foamed resin laminated therein. But, in the case of the automobile body panel having a relatively large area, it is required that a panel having a large area can be formed without generating creases or cracks. For that reason, there is a problem of enhancing the formability of a laminated plate in which an foamable resin in an unfoamed state is laminated.
On the other hand, there is further proposed a foamed resin laminated soundproof plate which is not limited as to the shape, mounting place and weight, is thin as a whole thickness of a laminated plate, is good in plastic working such as press forming, is provided with, for example, a sufficient damping performance in a final use state after going through a heat foaming step and exhibits a soundproof performance and, a method for manufacturing the same (see Patent Document 3).
In such a foamed resin laminated soundproof plate, so far as a resin having foamable property is kept in an unfoamed state, the thickness of the laminated plate can be made thin. For that reason, after the laminated plate having this foamable resin in an unfoamed state laminated therein is formed into a prescribed panel shape by press forming or the like, it is possible to increase the thickness of this composite panel by heating it at a resin foaming temperature to form the resin having foamable property into a foamed resin. Consequently, it is possible to perform press forming in a prescribed shape while ensuring dimensional and shape precision without being limited as to the shape, mounting place and weight as a laminated plate. Also, by increasing the thickness of the foamable resin, it is possible to enhance a rigidity imparting effect or a damping performance and to exhibit a soundproof performance.